Near-infrared (SWIR) or short-wave infrared light is generally defined as light with a wavelength range from 0.9 to 1.7 μm, but it can also be classified as light with a wavelength range from 0.7 to 2.5 μm. Since the human eye cannot directly perceive infrared light, we need to rely on instruments to obtain the information generated by infrared light.
Short-wave infrared imaging has unique advantages. It enables users to "see" things beyond the "visible range" of ordinary imaging. For example, when detecting fruits, there may seem to be no defects in the fruits from visual imaging, but in short-wave infrared imaging, the bruises inside the fruits can be clearly visible. Another example is when detecting the amount of filler inside opaque packaging. Using SWIR short-wave infrared lenses, one can "see" the filler inside the bottle.
Short-wave infrared imaging is widely used in multiple fields. It can be used to detect the drying uniformity of paint or bulk materials, inspect electronic panels, examine solar cells, and remotely monitor the temperature and uniformity during the metal smelting process, etc. The principle lies in that the "illumination effect" of short-wave infrared light is the same as that of visible light. Short-wave infrared light is reflected or absorbed by objects, which can provide a strong contrast and thus support higher-resolution imaging. In addition, environmental starlight and background radiation (atmospheric glow) are natural short-wave infrared radiation sources, which can provide excellent illumination for outdoor or nighttime imaging, including through fog, smoke and water vapor.
II. Imaging Characteristics
High Recognizability:
SWIR imaging is mainly based on the principle of imaging by the reflected light of the target, which enables it to present imaging features similar to those of visible light grayscale images. In this imaging mode, the contrast of the image is extremely high, and the details of the target can be clearly expressed. For target recognition tasks, SWIR imaging technology has become an important supplement to thermal imaging technology. For example, in complex environments, thermal imaging may be affected by factors such as insignificant temperature differences, while SWIR imaging can accurately identify the target object by virtue of its high contrast and clear presentation of details. Whether it is the recognition of tiny components in industrial inspections or the identification of specific targets in the security field, the high recognizability of SWIR imaging plays a crucial role.
All-Weather Adaptability:
SWIR short-wave infrared lenses are minimally affected by atmospheric scattering during the imaging process. This means that they can maintain stable imaging performance even under harsh climatic conditions. Their powerful ability to penetrate smoke, fog or haze enables them to effectively detect target objects in these adverse environments and also have a relatively long effective detection range. Compared with visible light imaging, SWIR short-wave infrared lenses have significantly better adaptability to climatic conditions and battlefield environments. In a port filled with thick fog, visible light imaging may fail to clearly capture the target due to the interference of fog, but SWIR short-wave infrared lenses can penetrate the fog and accurately monitor the position and status of ships. On the battlefield, smoke and dust often affect the vision of combat personnel, while SWIR short-wave infrared lenses can provide commanders with crucial intelligence information in such environments.
Low-Light Night Vision:
Under the night vision conditions with atmospheric glow, the photon irradiance is mainly distributed within the SWIR band range of 1.0 - 1.8 μm. This characteristic gives SWIR night vision imaging a significant inherent advantage. It can extract image details from deep shadows and can also image through window glass, which is very practical in some special application scenarios. For example, during nighttime monitoring tasks, when it is necessary to observe the indoor situation, SWIR night vision imaging can clearly capture the indoor dynamics through the window glass without the need to enter the room or break the window. This characteristic makes it particularly suitable for use in the dark or at night, providing strong support for nighttime security and reconnaissance tasks.
Covert Active Imaging:
In the band range of 0.9 - 1.7 μm, military laser light source technologies are mature (such as 1.06 μm and 1.55 μm). This gives SWIR imaging a significant comparative advantage in covert active imaging applications. In military operations, concealment is of vital importance. SWIR imaging can utilize mature military laser light sources to conduct active imaging without being detected by the enemy. By emitting laser light with specific wavelengths, the SWIR imaging system can obtain the reflected light of the target object and then generate clear images. This imaging method can not only effectively detect targets in the dark but also avoid being discovered by the enemy's reconnaissance equipment, thus improving the security and success rate of operations.
Simple Optical Configuration:
SWIR light can penetrate glass. This characteristic makes the optical configuration of SWIR cameras very simple. It does not require a special housing. Only a protective window glass needs to be assembled. This provides great flexibility when applied to specific platforms or occasions. For example, in some occasions where real-time monitoring of specific areas is required, such as laboratories, factory workshops, etc., SWIR cameras can be installed beside windows to conduct imaging through the glass without the need to modify the windows or install complex optical equipment. This simple optical configuration not only reduces costs but also improves the reliability and stability of the system.
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